Apple Macbook pro A1278 No green light no fan

[sureshbobby]

Hi friends need help
Macbook pro a1278 motherboard issues
No green light No fan runs
How to solve it

[mon2]

Re: Apple Macbook pro A1278 No green light no fan

Hi. What is the 820-xxxx logic board number?

Are you using a known good power adapter?

What is the history of the computer? Liquid damage?

Just stopped working?

[sureshbobby]

Re: Apple Macbook pro A1278 No green light no fan

Yes am using a original adapter it is working fine i have checked with another macbook.
Motherboard number is 820-3115

[mon2]

Re: Apple Macbook pro A1278 No green light no fan

Review page # 3 of the schematics. This page details the ordering of the power rails. Check each stage and post the first rail that is missing.

So for example, check that the DCIN from the adapter is reaching the fuse @ F6905. Then check AFTER this fuse to confirm the fuse is not blown.

Next, check the output of the dual diode @ D6990 (pin 3). Voltage here ?

Only if the voltage @ D6990 is high enough, then U6990 can perform its job of creating the required 3v42 rail.

Measure and post the voltage @ PP3V42_G3H_REG.

Voltage of PPBUS_G3H ?

[sureshbobby]

Re: Apple Macbook pro A1278 No green light no fan

Hi
Thanks for the reply it very helpful
i have checked the voltages of the Fuse D6990, U6990 they are getting 16.8v
i dont know what to do as am very basic learner of macbook

[mon2]

Re: Apple Macbook pro A1278 No green light no fan

Measure and post the voltage @ PP3V42_G3H_REG.

Voltage of PPBUS_G3H ?

[sureshbobby]

Re: Apple Macbook pro A1278 No green light no fan

PPBUS_G3H from 0.8 it is decreasing

[mon2]

Re: Apple Macbook pro A1278 No green light no fan

See attached.

1) Leave meter in DC voltage mode. Check the voltage @ F7040, pin # 1.

What is the reading ? Is it still ~0v8 ?

If the voltage is not the same as on F7040, pin # 2 then F7040 is blown and needs to be replaced.

2) If the voltage is about the same on both sides of F7040, then there is a fault on this switching regulator and may be due to a short circuit on the rail.

Remove all power (no adapter / no battery).

Meter in resistance mode (2k is ok but can be higher).

Red meter probe on F7040, pin # 1. Black meter probe on ground. What is the reading ?

Repeat for F7040, pin # 2.

This test is to check if there is a part that has failed (ie. shorted capacitor) and causing this power supply to shut down.

Update:

Attaching where to locate PP3V42_G3H_REG . Measure and post this very important voltage rail. It should be ~3v42 for this logic board.

[sureshbobby]

Re: Apple Macbook pro A1278 No green light no fan

same voltage on f7040 both pins
i measured resistance it is showing 0 ohms and no short here

[mon2]

Re: Apple Macbook pro A1278 No green light no fan

The resistance measurement should be RED meter probe on fuse pin & BLACK meter probe to ground.

Using this setup and meter on 2k or higher - you are reading 0 ohms ? If yes, then you DO have a short to ground.

Please confirm.